This invention relates to optical readers and in particular to optical readers including means for sweeping a light beam across a target and sensing the light signals reflected from the target.
In certain applications, such as a bar code reader, it is desirable and/or necessary to scan, or sweep, a light beam across a target, such as a bar code, and to sense light signals reflected from the bar code to subsequently decode the information encoded in the bar code. FIG. 7A illustrates the format a bar code may have (parallel bars of different widths and spacing) and a laser light beam sweeping across the bar code (i.e. the target). A known method for sweeping a light beam across a bar code includes a stepper motor used to turn a mirror arrangement as shown in FIGS. 7B and 7C. A light source which may be a laser or a light emitting diode (LED) is beamed onto the surface of the mirror. The mirror is rotated beta degrees by the stepper motor which causes the light beam to sweep through an angle of two beta degrees across a target (e.g. a bar code).
Another method for sweeping a light beam across a target includes the use of a miniature motor attached to a polygon mirror whose rotation is controlled by the motor, as shown in FIGS. 7D and 7E. Each surface or face of the "rotating" polygon is highly polished and functions as a mirror causing a light beam incident on the surface of the polygon to sweep across the target.
FIG. 7E shows the polygon mirror (pm) and the rotating driving motor (dm) which are independently constructed and respectively connected directly, or through a speed deceleration or reduction mechanism, with a rotating driving axis.
FIGS. 7B and 7C show the single plane/face mirror (m) and the stepper motor (gm) which are independently constructed and respectively connected with a rotating driving axis.
Normally, the polygon mirror (pm) and the rotating driving motor (dm) used for the light beam scanning arrangement as per FIGS. 7D and 7E are constructed as separate and independent elements. Consequently, the size and in particular the height (i.e., the dimension in the direction of the rotating and driving axis) cannot easily be reduced. Also, as the rotating driving motor (dm) is used, the dimension of the direction in the front and the rear (the dimension in the direction perpendicular to the direction of the rotating driving axis) cannot be easily reduced.
Similarly, the single plane/face mirror (m) and the stepper motor (gm) used for the light beam scanning arrangement as per FIGS. 7B and 7C are constructed as separate and independent elements. Consequently, the height (the dimension in the direction of the rotating driving axis) cannot easily be reduced. Also, as the stepper motor is used, the dimension of the direction in front of and the rear (the dimension in the direction perpendicular to the direction of the rotating driving axis) cannot be reduced easily.